1. Technical Field
The present disclosure relates to a wafer-level packaging of an integrated device of a MEMS (MicroElectroMechanical System) type, hereinafter “MEMS integrated device”.
2. Description of the Related Art
In the field of integrated devices, the need is certainly felt to reduce the dimensions to meet increasingly stringent requirements of miniaturization, in particular, in the field of portable apparatuses, such as, for example, smartphones, tablets, or PDAs.
In a known way, a MEMS integrated device generally comprises a first body (usually defined as “die”) including semiconductor material (in particular, silicon), integrating a micromechanical structure, operating, for example, as a sensor for one or more quantities to be detected (for example, for providing a pressure sensor or a microphone) and generating an electrical quantity that is a function of the quantity to be detected (for example, a variation of capacitance, a variation of electrical resistance, etc.). As it is known, the die is the result of an operation of sawing or singulation of a wafer, where a plurality of elementary devices are simultaneously provided during the manufacturing process.
A MEMS integrated device further comprises at least one second die including semiconductor material (in particular, silicon), integrating at least one electronic component or circuit, designed to be electrically coupled to the micromechanical structure so as to functionally cooperate therewith. Typically, the second die integrates an ASIC (Application-Specific Integrated Circuit) electronic circuit, electrically coupled to the micromechanical structure, operating, for example, as a reading circuit for reading the electrical quantity detected by the micromechanical structure in the case where the latter operates as a sensor (for example, for carrying out amplification and filtering operations of the same detected electrical quantity). The ASIC electronic circuit may also have further functions for processing and evaluation of the detected quantities, providing more or less complex integrated systems, so-called SiPs (Systems-in-Package).
A MEMS integrated device also generally includes a package, i.e., a container that surrounds, totally or in part, the dice of the device, ensuring protection thereof from external agents and enabling electrical connection towards the external environment. The assembly of the MEMS integrated device, inside the corresponding package, is usually defined as a whole as “chip”, and may, for example, be electrically connected to a printed circuit board of an electronic apparatus in which the MEMS integrated device is to be used.
In particular, when the micromechanical structure has deformable elements, for example, a beam or a membrane, which are designed to undergo deformation as a function of the quantity to be detected, the package includes a covering structure, or cap, defining at least one cavity, provided in a position corresponding to the same deformable elements in such a way as to create an empty space that ensures their freedom of movement and does not alter their deformation. Moreover, an access opening is possibly provided through the covering structure, if a fluidic connection with the outside world is required (for example, for entry of pressure or acoustic waves).
A known package structure, defined as a “wafer-level package”, is particularly advantageous in the case of portable applications in so far as it allows achieving resulting dimensions that do not depart significantly from those of the dice that are packaged. In short, the corresponding packaging technique envisages use of standard dice micromachining processes also for obtaining the corresponding package, providing at a wafer level, i.e., before the corresponding singulation operation, also the structures for covering and protecting the dice and the corresponding electrical and/or fluidic connections towards the outside environment, thus simplifying and uniforming the overall manufacturing process.
In the case of membrane micromechanical structures or the like (i.e., including further or different deformable elements), the required presence of a cavity entails that a desired reduction of the resulting package dimensions is, however, difficult to obtain, due, e.g., to the thickness requirements for the walls of the cavity, often provided in a composite substrate of a BT (Bismaleimide Triazine) type, having the function of covering structure. In addition, a marked reduction of the dimensions entails a greater difficulty in the manufacturing steps of the covering structure closing the cavity at the top, and major problems linked to mismatches in the thermal expansion coefficients of the materials used.
In general, problems of reliability and stability of performance may arise as the dimensions of the package decrease, which may jeopardize the operation of the resulting integrated devices.
The need is thus felt in the field to improve and further simplify the packaging techniques of MEMS integrated devices, in particular for the purposes of size reduction in the case where membrane micromechanical structures (or the like) are present.